WASHINGTON (AP) — Homeland Security Secretary Jeh Johnson is asking government lawyers to review how the Obama administration releases some criminal immigrants who are facing deportation.

Johnson told the Senate Judiciary Committee on Wednesday that lawyers will review federal policies based on a Supreme Court ruling that requires the government to release immigrants convicted of crimes if the U.S. can’t send them to their home country within six months. Johnson said he wants to know whether the government can hold them longer as threats to national security or public safety. He also said he wants more-senior officials to review and approve such releases.

Last month, the Obama administration acknowledged it has released more than 36,000 criminal immigrants living in the country illegally, including those accounting for 193 homicides and 426 sexual assaults.